1. Field of the Invention
The present invention relates to a liquid supply device, a liquid discharge device, and an image recording apparatus, and more particularly, to a pressure control technique for supplying a liquid to an ink jet head or the like.
2. Description of the Related Art
In order to stably operate an ink jet head and to stably supply an ink to the ink jet head, it is necessary that the internal pressure of the ink jet head or the pressure of an ink passage are controlled to be constant. As a means for controlling such pressure, a pump provided in the ink passage is used. On the other hand, when the internal pressure of the ink jet head or the pressure of the ink passage are controlled using the pump, a pressure change caused by the pulsatile flow of the pump may occur. The pressure change not also becomes an obstacle to stable ink supply but also disturbs the stable operation of the ink jet head.
On the other hand, a technique of providing a damper in an ink passage and suppressing a pressure change in the ink passage or a change in the internal pressure of an ink jet head is known. For example, a technique of varying the capacity of a sub-tank that communicates with the ink passage to function as a damper that suppresses the pressure change in the ink passage is known.
In JP2009-101516A, there is disclosed an inkjet recording apparatus including a recording head; first and second liquid chambers which communicate with the recording head; first and second communication passages which causes the first and second liquid chambers to communicate with a liquid buffer chamber, respectively; first and second pressure detecting means for detecting internal pressures of the first and second liquid chambers; a liquid moving means for causing a liquid to move between the first liquid chamber, the second liquid chamber, and the liquid buffer chamber; and pressure control means for controlling the liquid moving means so as to cause an inside of each of the first and second liquid chambers to become a predetermined pressure according to the detection results of the first and second pressure detecting means, and controlling the liquid moving means so that a predetermined pressure difference is set between the first liquid chamber and the second liquid chamber and a predetermined back pressure is applied to a liquid inside the nozzles of the recording head, thereby adjusting internal pressures of the first liquid chamber and the second liquid chamber, wherein two sub-tanks each of which has a liquid chamber and a gas chamber formed by dividing a sealed container by a flexible membrane are provided, and of the two sub-tanks, the liquid chamber of one sub-tank is the first liquid chamber and the other liquid chamber is the second liquid chamber.
According to JP2009-101516A, a pressure change caused by the movement of the liquid may be attenuated by the flexible membrane and the gas chamber. Accordingly, the pressure change is not transmitted to the recording head, and thus good printing quality may be ensured and pressure adjustment can be achieved with high accuracy.